<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>border实现圆角效果</title>
    <style>
        .rounded-button {
            position: relative;
            display: inline-block;
            padding: 12px 24px;
            background-color: #2396ef;
            border: 0;
            color: #fff;
            cursor: pointer;
        }
        .rounded-button::before,.rounded-button::after {
            content:"";
            position: absolute;
            left: 0;
            right: 0;
            border-style: solid;
        }
        .rounded-button::before {
            top: -4px;
            border-width: 0 4px 4px;
            border-color: transparent transparent #2396ef;
        }
        .rounded-button::after {
            bottom: -4px;
            border-width: 4px 4px 0;
            border-color: #2396ef transparent transparent;
        } 
    </style>
</head>
<body>
    <button type="button" class="rounded-button">圆角为4px的圆角按钮（border实现）</button>
</body>
</html>